1. Field of the Invention
The present invention relates to a dimming apparatus, and more particularly to an energy-saving dimming apparatus.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating the configuration of a general dimming apparatus. FIG. 2 is a waveform diagram of signals outputted from the dimming apparatus of FIG. 1. As shown in FIG. 1, such a general dimming apparatus includes a luminance-controlling dimmer 10, and a ballast 20 for continuously supplying an AC voltage to a load, that is, a discharge lamp 30. The dimmer 10 serves to continuously vary the luminance or color of a light source such as a lamp. Typically, the dimmer 10 is designed to generate a voltage Vd(t) shown in FIG. 2 using an auto transformer, or to generate a voltage Va(t) shown in FIG. 2 using a silicon controlled rectifier (SCR) or a triac, so as to supply the generated voltage to the ballast 20.
However, the general dimming apparatus shown in FIG. 1 has various problems.
That is, where an auto transformer is used to decrease an input voltage Vi(t) to a voltage Vd(t), there is a problem in that it is impossible to achieve an instantaneous voltage control. Although the auto transformer may use a tap changer adapted to cope with a variation in the input voltage Vi(t), it is inefficient in terms of energy saving because it involves loss of power.
Where the dimmer 10 is configured using a semiconductor element such as an SCR or triac, a peak current Ipeak is generated when the semiconductor element is switched, as shown in FIG. 2. Such a peak current may fatally affect neighboring devices. That is, the dimmer 10, which uses a semiconductor element, allows the input voltage Vi(t) to pass therethrough only during a period from t1 to t2 and a period from t3 to t4 within one cycle of the input voltage Vi(t)., in order to supply the voltage to the ballast 20. In this case, however, a peak current is generated at the switching points t1 and t3. This peak current may exhibit an interference effect adversely affecting other electric appliances (for example, neighboring discharge lamps).
Furthermore, in the case of the dimmer using an SCR or triac, it is difficult to achieve a desired power factor correction. For this reason, it is difficult to expect a desired energy saving effect. That is, the dimmer 10 cannot adjust the phase difference θ between voltage and current to be constant, as shown in FIG. 2, so that it is difficult to achieve a desired power factor correction. As a result, the efficiency of saving energy is lowered.